TEM接收机低噪声抗饱和前放电路设计

Design of low-noise and anti-saturation preamplifier for the transient electromagnetic receiver

为了满足瞬变电磁接收机的低噪声要求及消除在瞬变信号早期易出现饱和的现象 ,设计了 TEM接收机低噪声抗饱和前放电路 ,该电路使用超低噪声运算放大器 LT1 0 2 8,并采用屏蔽接地技术降低外部地干扰、耦合等噪声 ;使用可编程放大器 PGA2 0 2对整个瞬变信号采用分段放大技术 ,既避免了早期信号饱和 ,又保证了接收机的动态范围。该设计电路还可用于其他大动态信号采集系统中。实践证明 ,该电路改善了整机的信噪比 ,提高了晚期微弱信号的识别能力 (检测的有效信号为几个微伏 ) ,在具体应用中取得了良好的效果。

In TEM (Transient Electromagnetic Methods), in order to reduce the noise of preamplifier to improve the detection capability of receiver for weak signal in late period and eliminate the saturation for large signal in early period, the low-noise and anti-saturation preamplifier circuit for the Transient Electromagnetic receiver was designed. The low-noise preamplifier was made up by three ultra low noise precision high speed Op Amps name LT1028.Through the electromagnetism shielding and grounding, the interference and noise was reduced. The digitally controlled programmable-gain instrumentation amplifier named PGA202 provided different gains at different periods of transient signal to eliminate the saturation as well as keep the dynamic range of the TEM receiver. The preamplifier can also be used in other large dynamic range signal acquisition systems. The experiment result proved that the preamplifier improved the SNR(Signal-to-Noise Rate) and the capability of distinguishing the weak available signal from noise in late period of transient signal.